1. Field of the Invention
The present invention relates to a fixing apparatus which is used in an electrophotographic image forming apparatus such as a copying machine or a laser printer and configured to fix an unfixed toner image formed on a recording material to the recording material by heating and pressurization.
2. Description of the Related Art
As a fixing apparatus to be used in an electrophotographic image forming apparatus, there is used a film fixing type fixing apparatus that is superior in on-demand property.
A film fixing type fixing apparatus includes a tubular film, a heater held in contact with an inner surface of the film, and a pressure member forming a nip portion together with the heater through the intermediation of the film. A recording material which bears a toner image is heated at the nip portion while being conveyed, so that the toner image is fixed to the recording material.
In order to quickly raise the film temperature to a target temperature, a film heating type fixing apparatus uses a film of small heat capacity. As the film material, there is used a metal material such as a stainless steel or nickel, or a heat resistant resin material such as polyimide. Generally, a metal material has a higher strength as compared with a resin material, so that it allows thinning. Further, the metal material has a higher heat conductivity. On the other hand, a resin material has a smaller specific weight as compared with metal, and has small heat capacity, so that it can be easily warmed. Further, a resin material can be formed into a thin film through coating molding, so that resin material can be molded at low cost.
In the film heating type fixing apparatus, due to a design tolerance, or the like, deviation in a degree of parallelization between the pressure member and the film or a difference in pressurization force between the right and left sides may occur. In such cases, deviation of the film may occur in a direction orthogonal to a recording material conveyance direction of the film (hereinafter, this will be referred to as film deviation).
Japanese Patent Application Laid-Open No. 2002-246151 and Japanese Patent No. 3814542 discuss a configuration in which an end portion of a film is received by a regulation surface of a regulation member and in which some improvement is added to a shape of the end portion of the film, so that the film deviation is regulated, and it is possible to prevent damage of the end portion of the film such as bending or cracking in the end portion of the film through its flaring.
However, from the viewpoint of the recent demand of energy saving for friendliness to environment, a further reduction in power consumption is required of the fixing apparatus. To reduce the power consumption, it is effective to enhance the heat transfer efficiency from the film to the recording material, so that a further reduction in film thickness is in progress. Thus, a shortage of the strength of the end portion of the film is to be expected.
Thus, when a further reduction in film thickness is achieved, the regulation member as discussed in Japanese Patent Application Laid-Open No. 2002-246151 and Japanese Patent No. 3814542 may be insufficient as a countermeasure against damage of the end portion of the film. Because, in the regulation member discussed in Japanese Patent Application Laid-Open No. 2002-246151 and Japanese Patent No. 3814542, there is a fear of the end portion of the film being inwardly bent if a force toward an inner surface direction is applied to the end portion of the film when the film moves to a radial direction due to film deviation.